Final answer:
Thermal biology involves the study of how marine fishes and invertebrates regulate their body temperature and adapt to various thermal conditions in marine environments.
Step-by-step explanation:
The subject of thermal biology of marine fishes and invertebrates encompasses the study of how these organisms regulate their body temperature in a marine environment, particularly the mechanisms and behaviors that allow them to survive in various thermal conditions. Fishes have structural adaptations like stream-lined bodies to reduce water resistance, gills for respiration in water, and fins for movement. Marine invertebrates, which include some of the most commonly introduced species worldwide, face challenges such as maintaining water and solute balance due to the surrounding environment's high solute concentration. They exhibit morphological and physiological changes to adapt to their saltwater habitat, such as the marine iguanas that excrete salt through sneezing while maintaining internal solute concentrations. The presence of both marine organisms near underwater volcanoes and in hydrothermal vents indicate adaptations to extreme thermal environments, suggesting a variety of strategies to cope with varying temperature regimes.